Magnification viewers are well known in the art and generally comprise one or more optical loupes coupled to eyeglass frames or headbands. Such magnification viewers are often worn by physicians for extended periods of time during clinical procedures so as to provide clarity of view and a magnified image of the body part of interest, while avoiding a “hunched over position” that can result in debilitating neck and back strain, and which can consequently have an adverse effect on the success of an operation. By permitting the physician to operate at a greater working distance from the patient, magnification viewers also reduce the physician's exposure to potential contamination from aerosols.
Since physicians use magnification viewers during surgery and other procedures requiring manual precision over extended periods of time, it is important that they be lightweight, comfortable, and provide good clarity and a wide field of vision while providing high resolution.
The optical loupes of clinical magnification viewers are often made according to the Galilean telescope design, having a single objective lens and a single eyepiece lens. Galilean telescopes are characterized by relatively narrow fields of view that are mainly limited by the diameter of the objective lens. The basic Galilean design, however, produces substantial chromatic aberration (“colouring”) and lack “edge to edge” clarity. Thus, image quality is poor.
The chromatic aberration of the basic Galilean design may partially be overcome by combining convex and concave lenses with different refractive indexes. However, this addition of further lenses increases the weight of the loupe and the magnification viewer.
Another well known loupe design is the so-called Keplerian design which uses prisms to enhance “edge to edge” clarity and to provide higher magnification values than the basic Galilean design. The additional prisms, however, add to the weight of the individual loupe element and, thus, of the magnification viewer.
Aspherical lenses have long been known in the art and exhibit much less chromatic aberration and provide superior “edge to edge” clarity as compared to the conventional lenses typically used in the Galilean design. Aspherical glass lenses, however, are even nowadays difficult to grind and polish and are thus expensive. Aspherical plastic lenses can be produced by injection moulding and are, thus, much cheaper in production than aspherical glass lenses as soon as a casting mould is available. Plastic lenses, however, suffer from other disadvantages, namely that they are prone to mechanical, heat or chemical damage. In other words they are easily scratched, scuffed, affected by organic solvents or otherwise damaged, especially during cleaning and have been perceived as not suitable to be used the harsh clinical environment requiring aseptic conditions. Accordingly, aspherical plastic lenses have not been used in clinical settings as of yet.
In summary, a need exists for improved magnification loupes and magnification viewers, particularly for use in clinical applications, which are light-weight and provide good edge to edge clarity.